1. Field of the Invention
The invention relates to the field of permanently implantable devices for intraoperative positioning and subsequent fixing of active or passive implantable actuator or sensor in a human body, especially in the mastoid and middle ear area of the skull.
2. Description of the Related Art
In view of the extraordinarily small and sensitive anatomic structures in the human body, especially in the mastoid and middle ear area of the skull, it is almost impossible to hold an actuator or a sensor in position by hand for longer than a few seconds and to do so would require a considerable expenditure of strength and concentration by the surgeon. However, many surgical procedures in the body, especially in the skull area, requires targeted positioning of suitable actuator or sensor over long time intervals.
As a result, hand-guiding of actuator and sensor during microsurgical, therapeutic or diagnostic manipulations of such small sensitive structures, for example of the skull, always entail the risk that as a result of the possible relative movements between the hand-guided means and the body of the patient, these target structures are damaged or changed under certain circumstances. Thus, in such medical techniques, there has long been a need for a positioning and fixing system which can be anchored stationary on the body, especially on the skull, by means of a holding device.
Various implantable actuator holding devices are known from the prior art. A holding device, as a component of a partially implantable piezoelectric hearing aid for stimulating the stirrup, was presented by N. Yanigihara, K. Gyo and Y. Hinohira in the article Partially Implantable Hearing Aid Using Piezoelectric Ceramic Ossicular Vibrator which appeared in Otolaryngologic Clinics of North America, Vol. 28, No. 1, February 1995, pages 85-97. The external part of the device is made like a conventional, behind-the-ear hearing aid and contains a microphone, amplifier, battery and the external transmitting coil. The internal part of the device which is fixed on the skull, is used to hold the inner receiving coil. For positioning and fixing of the piezoelectric bimorph converter in the middle ear, there is a relatively simple L-shaped, bone-anchored fastening element. The fastening element is a retaining sheet which can be fixed on the skull cap with two bone screws and is composed of a metal plate with two elongated holes and a wire axle attached vertically thereto. After the metal plate is screwed onto the skull cap, the wire axle points toward the middle ear (medially). On the wire axle, a sleeve can be axially pushed and thus, the piezoelectric bimorph converter can be positioned by fastening it to the sleeve. This enables one axial and one rotational degree of freedom on the wire axle. After disintegrating the hammer and the anvil, the free end of the piezoelement can be fastened preferably directly on the stirrup head with cyanoacrylate cement.
Another holding system for an actuator implant module which improves hearing was described by J. Frederickson, J. M. Coticchia and S. Khosla in the article entitled Ongoing Investigations Into Implantable Electromagnetic Hearing Aid for Moderate to Severe Sensorineural Hearing Loss which also appeared in Otolaryngologic Clinics of North America, Vol. 28, No. 1, February 1995, pages 107-119. This holding system is a component of a partially implantable electromagnetic hearing aid which had been tested previously in an animal model. For its implantation, a small hole is made in the anvil body with a surgical laser to attach a permanent magnet. The laser head is guided in this case in a threaded sleeve with an inner and an outer thread which has been screwed into the mastoid bone, the longitudinal axis of the threaded sleeve pointing to the anvil body. After the laser hole is made in the anvil and the laser head is removed, the electromagnetic drive (xe2x80x9ctransducer probe tipxe2x80x9d) can be screwed into this threaded sleeve and positioned medially to the magnet which is attached to the ossicle.
Another holding system was developed by Maniglia et al. for a partially implantable electromagnetic middle ear stimulator as described in Contactless Semi-Implantable Electromagnetic Middle Ear Device for the Treatment of Sensorineural Hearing Loss by A. J. Maniglia, W. H. Ko, M. Rosenbaum, T. Falk, W. I. Zhu, N. W. Frenz, J. Werning, J. Masin, A. Stine and A. Sabri as published in Otolaryngologic Clinics of North America, Vol. 28, No. 1, February 1995, page 121. Here, a small magnet is cemented to the anvil using surgical cement. The drive coil can be positioned along a titanium guide shaft which can be implanted in the mastoid up to an air gap of a maximum 1 mm to the permanent magnet which is attached to the ossicle. This titanium shaft has, like in the device of Yanigahara et al., two elongated holes and an additional drill hole for fixing by means of three bone screws on the skull cap. By means of a threaded axle, an electronic module and the drive coil attached thereto, can be positioned medially in an elongated hole guide and can be fixed via a screw with a lock nut on the shaft.
The above described prior art holding systems are used for permanent fixing of the components of the hearing aid on the skull bone or in the vicinity of the middle ear and inner ear. Overall, they exhibit an extremely limited intraoperative positioning capacity due to the absence of useful degrees of freedom. In addition, they must all be matched to the anatomic circumstance of the implantation site and to the pre-established location of the target point in the middle ear by more or less precisely manually bending. Two of the above described holding systems also require the use of an adhesive or surgical cement to fix a component of the device and are often not suited as long term implants due to losses in adhesion strength.
U.S. Pat. No. 5,788,711 discloses an implantable, fixable positioning system for secure linkage to the human body, especially to the human skull, which can be permanently attached without adhesives or surgical cements or without manually bending the implant holder. This system allows positioning of surgical, therapeutic or diagnostic sensors or actuators in the body free of relative motions, and fixes them securely in the established position. This system is provided with a holding device which can be fixed on the human body, a ball joint attached to the holding device by a clamp mechanism, and be manually positioned using an auxiliary tool. A guide rail is permanently connected to the ball of the ball joint and a threaded spindle is pivotally mounted in the ball and within the guide rail but the spindle cannot move axially. A carriage is guided in the guide rail and on the threaded spindle for an axial adjustment motion. In this regard, the system includes a feed nut which is secured against rotary motion relative to the guide rail and engages the threaded spindle by the threads. The feed nut can be freely positioned by turning the threaded spindle by means of an auxiliary tool along the guide rail. The system also includes a receiver which is attached to the carriage of an implantable device to be positioned or fixed. This positioning and fixing system has proven especially effective in practice in the implantation of hearing aids. However, further improvements are desired with respect to guide accuracy and ease of use.
Therefore, there still exists an unfulfilled need for an improved system which can be permanently attached to the human body free of relative movements and to fix implantable device in the ascertained position more accurately and for such a system which is more easily used.
The primary objects of the present invention is to provide an improved implantable positioning and fixing system for positioning and fixing of an implantable device relative to a human body which is more accurate and more easily used.
These objects are achieved by providing a permanently implantable positioning and fixing system for positioning and fixing of an implantable device relative to a human body, comprising a plate member constructed to affix to the human body, a ball-and-socket joint having a socket attached to the fixing member and a ball positionably mounted in the socket, a clamp mechanism cooperating with the ball-and-socket joint for selectively fixing the ball relative to the socket, a guide rail which is fixed to the ball of the ball-and-socket joint, the guide rail including outer guide surfaces, a threaded spindle having an outer thread, the threaded spindle being mounted to rotate relative to the guide rail and to prevent axial movement of the threaded spindle, a carriage with a feed nut having an inner thread that is engaged by the outer thread of the threaded spindle in a manner that the carriage is freely positionable along the guide rail by turning the threaded spindle, the carriage including inner guide surfaces that slidingly engage the outer guide surfaces of the guide rail, and a receiver attached to the carriage for receiving an implantable device which is to be positioned and fixed in the human body.
In the positioning and fixing system in accordance with the present invention, relatively large-area contact surfaces can be achieved between the guide rail and the carriage. This acquires practical importance mainly when the overall dimensions of the system must be very small, such as is typically the case in devices which are to be implanted in the human body, for example hearing aids. A relatively large contact area between the guide rail and carriage results in comparatively low surface pressures. The reduction of friction between the components can thus be achieved thereby providing for easier adjustment of the carriage over the guide rail over the entire path of the carriage. The system is especially stable relative to transverse forces in the axial, radial, and angular direction.
The positioning and fixing system which is to be fixed permanently on the body is used with its receiver for any active or passive, actuator, sensory, mechanical or optical means as an xe2x80x9cartificial, tremor-free handxe2x80x9d of the surgeon to position, and then fix the free action end of the implantable device to a desired destination point on the body without risky relative movement occurring.
In one embodiment, the inner guide surfaces are formed preferably by the cheeks of the carriage which are elastically located in a plane perpendicular to the longitudinal axis of the threaded spindle with reference to the feed nut. In this way, mutual pressing force against the guide surfaces of the carriages and guide rails can be achieved. As a result of the elastic cheeks, the inevitable production tolerances are automatically compensated for. Play-free guidance, both in the radial, and also the angular direction, can be ensured. Assembly of the carriages and the guide rail under prestress is also possible. The effective prestressing force can thus be set by the corresponding choice of thickness and/or length of the elastic cheeks.
One especially compact and durable arrangement is obtained when the cheeks are molded onto the spring arms which are connected integrally to a carriage body which has the feed nuts.
In another embodiment of the present invention, the inner guide surfaces of the carriage and the outer guide surfaces of the guide rail are each arranged diametrically opposite one another in mirror symmetry to the longitudinal plane of the carriage which contains a longitudinal axis of at least one of the feed nut, the guide rail, and/or the threaded spindle. In addition, the inner guide surfaces of the carriage and the outer guide surfaces of the guide rail may be angled with respect to the longitudinal plane of the carriage, for example an angle in the range from 10 to 60xc2x0. The oblique positioning of the guide surfaces causes automatic centering of the carriage on the guide rail. The threaded spindle itself no longer needs to perform any guiding function thus, it is only used to position the carriage. Overall, ease of working is achieved with simultaneous high guidance accuracy.
In another embodiment, the feed nuts and the threaded spindles are preferably provided with self-locking threads, i.e. threads with a pitch dimensioned such that by turning the spindle, adjustment of the carriage can be caused but force exerted on carriage does not turn the spindle. In this way, unintentional movement of the carriage and the implantable device associated with it can be easily and reliably prevented.
One end of the threaded spindle is rotatably supported in the ball and another end of the threaded spindle is rotatably supported by the guide rail.
Advantageously, the ball has an auxiliary tool receiving opening for attachment of an auxiliary tool which may be used to position the ball in the ball-and-socket joint, while the threaded spindle, on its end facing the ball joint, has a receiving opening for attaching a tool for rotating the spindle. Here, the arrangement is such that these receiving openings are arranged coaxially to one another and the receiving opening for attaching the tool used to turn the threaded spindle is accessible through the auxiliary tool receiving opening which is used to position the ball.
To keep the number of parts small and to make handling especially simple, there may be provided a single actuator for actuating the clamp mechanism.
The clamp mechanism can be built in. various ways. In one embodiment, the clamp mechanism may be a wedge-clamp device with a pressure dome which slides on an oblique plane and be pressed against the ball by tightening a locking screw.
According to one modified embodiment, the clamp mechanism can be made as a ring clamp device with a clamp ring which can be screwed into a thread of the socket to press against the ball.
The clamp mechanism, however, can also be made as a lever-clamp device with a pressure dome which acts as the lever, the pressure dome being adapted to be swivelled around a lever thrust bearing and be pressed against the ball by tightening a locking screw.
Another suitable embodiment of the clamp mechanism is a cam clamp device including a pressure dome and a cam disk torsionally attached to a locking screw, the cam disk being adapted to press the pressure dome against the ball when the locking screw is turned.
Furthermore, the clamp mechanism can be a clip-type clamp device where the socket is slotted to elastically surround the ball in a manner that the socket is pressed against the ball by tightening a locking screw.
The clamp mechanism can also be made as a thrust pin clamp device. Here, the clamp device may include a thrust pin which may be screwed into a threaded hole of the plate member and be pressed against the ball by rotating the thrust pin. According to one modified embodiment, the thrust pin can be pressed against the ball by swivelling a cam and can be elastically prestressed in the direction to the ball.
The actuator is preferably provided with a loss preventor which prevents the ball from unintentionally falling out of the socket.
The tool which may be used to turn the threaded spindle preferably has a spherical head with a polygonal profile which can be positively engaged with the receiving opening of the threaded spindle which has a complementary polygonal profile. The polygonal profile may be in the manner of a homokinetic joint (Torx(copyright)). In this way, the threaded spindle can also be safely turned when the space conditions at the implantation site do not allow alignment of the axis of the tool with the axis of the threaded spindle.
The positioning and fixing system can be made from biocompatible materials. Preferably, the positioning and fixing system may be made from implantable metals, for example, pure titanium, implantable alloys of titanium, and implantable steels.
The implantable device can be designed for diagnosis, therapy and/or for surgical applications for temporary or permanent implantation of these means. The implantable device may be an implantable electromechanical hearing aid converter, as is described, for example, in U.S. Pat. No. 5,277,694.
The positioning and fixing system can be designed for positioning and coupling a hearing aid converter attached thereto anywhere in the middle ear, including any coupling site to the inner ear such as an artificial or natural window, and for fixing the hearing aid converter in position. The destination point can be any point of the hammer, anvil or stirrup. The hearing aid converter can be an actuator component of a partially or fully implantable hearing aid.
The positioning and fixing system in accordance with the present invention may provide four degrees of freedom of positional adjustment for a free action end of the implantable device, one of the four degrees of freedom being an axial degree of freedom provided by the threaded spindle and three of the four degrees of freedom being provided by the ball-and-socket joint.
The instantaneous position of the ball and correspondingly, the three rotational degrees of freedom may be secured by frictional forces even when the clamp mechanism has been released.
To facilitate installation and adjustment of the positioning and fixing system for the surgeon, the controls for manual positioning of the ball-and-socket joint, the carriage and the clamp mechanism are positioned to give a surgeon unobstructed access and adjustment. In this regard, these controls may point away from the body of the patient towards the direction of surgeon. In this respect it has been found to be a good idea if the construction and geometrical dimensions of the positioning and fixing system are such that the surgeon, when working with the naked eye or when using a microscope, always retains an unobstructed view of at least the free action end of the implantable device and also of the implantation area together with the destination point in the body of the patient. In this way, the risks caused by possible mispositioning of the means is kept especially low for the patient.
The preferred region of the body into which the positioning and fixing system can be inserted along with the implantable device is the mastoid cavity which is located under the external ear in the skull bone. It can be opened using standard microsurgical techniques. The volume may be a few cubic centimeters but varies widely depending on the individual patient.
The plate member of the positioning and fixing system in this case, is screwed onto the surface of the skull bone which borders the edge of the mastoid cavity which was formed. The system is designed such that it does not project above the level of the arch of the cap. This ensures that the implanted system is not perceivable under the skin after the surgery.
This positioning and fixing system enables tremor-free intraoperative positioning and fixing of any implantable device including an actuator or sensor on one of the three ossicles of the chain of auditory ossicles (hammer, anvil, stirrup), on the bony partition between the air-filled inner ear (promontory), in the liquid-filled inner ear itself, or in the adjoining vestibular organ. Other applications of the system as claimed in the invention include brief, intraoperative laser surgery in the entire skull area including microcoagulations or tissue obliterations. When a measurement laser is coupled in, vibrations, for example of the chain of auditory ossicles, of the ear drum, or of the round window membrane, can be measured without contact, intraoperatively.
In one preferred embodiment of the invention, the implantable positioning and fixing system is combined with an actuator hearing aid converter which is used for vibrational stimulation of the hearing-impaired to improve hearing. In this embodiment, the converter can be a component of a partially or completely implantable hearing aid.
These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the invention when viewed in conjunction with the accompanying drawings.